Goals from Sean Rigg, Alfie Potter and Tom Craddock did the damage as Oxford, who had James Constable sent off midway through the second half, extended their unbeaten run to nine in all competitions.
And Ardley, who took the reins from Terry Brown in October, did not hold back as he laid in to his under-performing players after the full-time whistle.
"I've defended the players in the past and I'm not going to defend them after that," said Ardley.
"I work hard along side my backroom coaching staff for every game. We think about what we have to do in training, but ultimately when you get out on the pitch it takes us until we're 2-0 for anyone to show any courage.
"There are too many weak mentalities. We're bottom going into the new year and I'm willing to have a go at this and make sure we don't go down. I need players who can show a bit of courage and show some balls.
"You have players that know how to win games and you have players that don't. For 25 to 30 minutes, there wasn't one player who took responsibility for their performance. Not one player did their bit that they were asked to do before the game."